I tip barbers like taxi drivers where I throw in an extra £1 if I’m paying in cash. I think this makes me eccentric in the UK though; not sure it is normal to tip them. Usually don’t bother adding a tip if paying by card.
Restaurants have recently started adding a discretionary 10% service charge to bills in my city but that is the tip. Wouldn’t tip more than that. If they don’t include it in the bill I try to work out something like 12% from quick mental maths and add that on.
I’ve noticed the till checkouts have options to tip in some shops now but have never given any tips via the prompt.